Method for the shaping of fibres with assistance of electric charge

ABSTRACT

A method for manufacturing an absorbent structure in an absorbent product such as a sanitary napkin, panty liner, diaper or similar product, which is manufactured by air-permeable forming elements. In the present method, the constituent fibres or similar material are given a certain electrical potential while the forming elements completely or partially are given an opposite potential or are grounded, the position and duration of the potential being variable. The material&#39;s orientation, distribution and location can be controlled so that the structure in the absorbent product can have the desired appearance.

BACKGROUND

The present invention concerns a method for the manufacture of anabsorbing structure in an absorbent product, such as a sanitary napkin,panty liner, incontinence protector, diaper or similar article, which ismanufactured by means of air-permeable shaping elements, combined withthe use of electric potential differences.

TECHNICAL BACKGROUND

Many different designs of such absorbent products are known. Theabsorption body in such products is conventionally produced by drydefibrating cellulose pulp in the form of rolls, bales or sheets, andconverting it in fluffed-up form into a pulp web, sometimes with theinclusion of so-called super absorbents, that is, polymers with thecapacity to absorb several times their own weight of water or bodyfluids.

Pulp cores are often compressed, partly to increase their wickingability, and partly to reduce the bulk of the pulp core to achieve aproduct which is as compact as possible.

The absorption body can also include other components which can, forexample, increase its wicking ability as well as increase its resistanceto deformation during use. An example of such components is cellulosefibres which are stiffened by chemical or other means. Other examples ofsuch components are different types of connecting fibres.

A problem which occurs during the manufacture of these products is thatcurrent methods for forming webs of individual absorption structures arecomplicated. They are also limiting in speed, and limit the ability tomanufacture more complicated absorption structures having multiplelayers and with admixture of different types of for example superabsorbents, connecting fibres or such like.

In connection with this technical field, it is usual to use suction tofill moulds on a so-called web former with absorbent material bysupplying the mould with a mixture of air and absorbent material,whereby the air flows through the air-permeable surfaces and leavesbehind its load of absorbent material. As the layers of depositedmaterial are in themselves air-permeable, successive layers of materialcan be laid down until the moulds are filled. WO-A-90 05511 and EP 155752 show two arrangements which use such a method and which include suchmoulds. These arrangement further show rotating brush means for theremoval of surplus absorbent material which lies above the top level ofthe mould.

U.S. Pat. No. 4,675,144 shows an alternative arrangement formanufacturing an absorption body, whereby a web of fibres is built up onan endless air-permeable belt, called a wire cloth, in a manner similarto that described above. Absorption bodies are then cut out from thebuilt-up fibre web.

Further, EP 0,010,756 shows a process for manufacturing a non-wovenmaterial, whereby the fibres are given an electrical charge when theypass between two rollers between which an electrostatic field ispresent. The fibres are subsequently collected on a moving collectorsurface.

TECHNICAL PROBLEM

One problem with manufacturing the above-mentioned products by means ofsuch arrangements or similar arrangments is the difficulty ofcontrolling the distribution in the absorption body of the fibres orother absorption materials, such as polyacrylate, CMC, etc. Thisdifficulty can lead to undesirable density and thickness variations inthe absorption body. Furthermore, there is no control over theorientation that each fibre takes up in the absorption body which leadsto disadvantages such as uncontrolled directions of flow, poor tensilestrength in varying directions as well as reduced absorption capacity.

BRIEF DESCRIPTION OF THE INVENTION

The problem of controlling the material distribution and orientation issolved in the present invention by giving such materials, before theyarrive at the web former, a powerful electrical charge by means of anelectrostatic field which is generated as the material arrives, forexample by means of rotating wheels, a grid or similar means. Groundingthe web former moulds, either partially or wholly, produces potentialdifferences which can be used to control the placement of the materials.

By giving different materials different potentials, it is also possibleto arrange the three-dimensional distribution of the differentmaterials, which in turn leads to several advantages in connection withflow speed and direction. A further advantage with the present inventionis that the presence of air-born dust in the vicinity of the productionmachine is reduced.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a cross-sectional view from the side of a part of anabsorption body, in which a region of the absorption body contains"standing" fibres which positively influence the flow of liquids in thevertical direction.

FIG. 2 shows part of an absorption body seen from above, in whichsections through various planes in the body are visible in order toillustrate the orientation of the fibres in the different planes 1, 2and 3. The orientation of the fibres are similar to that of wood fibresin a so-called plywood sheet, and in this way high strength is achieved.

FIG. 3 shows part of an absorption body seen from above/from the side,to illustrate the possibility to control the exact location of a type offibre within the absorption body.

FIG. 4 shows a web former wheel with the accompanying web former hood,and a device for charging the absorbent material. Further, there isshown a zone, preferably grounded, located in the web former moulds.

DETAILED DESCRIPTION OF THE INVENTION

The inventive method is based upon the well known fact that elementswith different electro-magnetic potentials are attracted to one another.It is also known that the bigger the difference in potential between thetwo elements, the bigger the attractive force which occurs between saidelements. In the method according to the present invention, one elementor several elements lying beside or after one another, are located underthe web former. Said elements can even form different kinds of patterns,and possibly said elements can even be part of the web former itself.These elements are then given a determined polarity, preferably bygrounding. In a preferred embodiment, the base and possibly also thesides of the web former are in the form of a so-called lattice, that isa plurality of small discrete elements which can have their potentialscontrolled separately, for example by means of a PC. Fibres orcomparable material which are fed into the web former via one or morefeed ducts are given a charge which can be varied in strength and whichis opposite that on the above-named elements. By varying the extensionin time and space of the ground elements, and by varying the charge onthe fibres or comparable materials, it is possible to achieve a greatvariety of fibre distributions and orientations. Furthermore, it ispossible to control the placement of the fibres or similar material inyet another plane, the vertical plane, by the use of materials such aspolar fibre types etc., or fibres which have been made polar by asuitable treatment such as, for example, water coating.

In a pre-erred embodiment, the material which is to form the absorptionbody is charged to a potential when it is being introduced into the webforming area. The potential can vary from between 0,1 kV to 100 kVdepending on particle size, material, manufacturing speed, etc. Undercertain conditions, the potential can go up to 150-200 kV. FIG. 4 showsa web former hood 1 and a web former wheel 3. Fibres supplied to the webformer hood 1 are indicated by the arrow F. In this preferredembodiment, the material is given the desired potential by passing thematerial through a grid 2 of electrodes which are supplied by ahigh-voltage generator. Furthermore, some parts 5 of the web formermoulds 4 located in the web former wheel 3 are grounded, other parts areinsulated, and further parts are connected to another generator whichcan bring about a variable potential opposite to that produced by thefirst generator. In this way, the desired control of the material isbrought about.

We claim:
 1. A method for the manufacture of an absorbent structure inan absorbent product from one or more constituent materials, said methodcomprising:depositing a constituent material, from a mixture of air andsaid material, on an air-permeable forming element while drawing airthrough the forming element so as to form the absorbent structurethereon, controlling the depositing step to obtain selectiveorientation, distribution and placement of the constituent materialthroughout the absorbent structure, said controlling step includingelectrically charging the constituent material before it reaches theforming element, creating an electric field adjacent the formingelement, and thus creating potential differences between the constituentmaterial and the electric field adjacent the forming element such thatselective orientation, distribution and placement of the constituentmaterial is obtained.
 2. A method according to claim 1, wherein thepotential differences are brought about by grounded control elementsplaced under the forming element.
 3. A method according to claim 1,wherein the potential differences are brought about by grounded controlelements which are at least partially constituted by the forming elementitself.
 4. A method according to claim 2, wherein the potentialdifferences are brought about by varying the potentials over a period oftime.
 5. A method according to claim 1 wherein different constituentmaterials are deposited on the forming element, said charging stepincluding charging the different materials to different potentials.
 6. Amethod according to claim 1, further comprising varying the charge onthe constituent material.
 7. A method according to claim 3 wherein theconstituent materials are fed to the forming elements by one or morenozzles, whereby the constituent materials are given an electricalcharge by means of a charging means, placed in said one or more nozzles.8. A method according to claim 7, wherein the constituent materials arematerials which have with respect to each other different conductivity,size and shape.
 9. A method according to claim 1, wherein theconstituent materials are selected from the group consisting ofcellulose fibres, super absorbents, CMC, poly-acrylates andnon-absorbing connecting fibres.
 10. A method according to claim 6,wherein one or more of the constituent materials is polar.
 11. A methodaccording to claim 7, wherein said control elements form a pattern whichcorresponds to the desired material distribution in the absorbentstructure.
 12. A method according to claim 11, wherein said controlelement forms a lattice made up of many small discrete elements, and thepotential of each small discrete element is individually controlled. 13.A method according to claim 12, further including electronicallycontrolling the charge distribution for the lattice and for the chargingmeans placed in the nozzles.
 14. A method according to claim 13, whereinsaid electronically controlling step includes using a PC.
 15. A methodaccording to claim 1, wherein said electric field creating step includescreating a selective variation of the electric field within a boundaryof the forming element.
 16. A method according to claim 1, wherein thepotential differences are brought about by control elements of selectivepotential.
 17. A method according to claim 1, wherein the potentialdifferences are brought about by control elements of selective potentialwhich are at least partially constituted by the forming element itself.